(a) Field of the Invention
The present invention relates to a liquid crystal display (LCD) assembly, and more particularly, to an LCD assembly that can display colors with high chromaticity.
(b) Description of the Related Art
Generally, an LCD assembly employing a thin film transistor (TFT) as a switching element can display colors by controlling the TFT and an liquid crystal cell to adjust transmissivity of light emitted from a backlight and by additively mixing three primary light colors transmitted through red, green and blue color filters.
FIG. 1 is a sectional view of an LCD panel in a conventional LCD assembly. An LCD panel comprises a TFT substrate 200 having TFTs corresponding to a plurality of pixels, a color filter substrate 100 having the color filters 300, and a liquid crystal 400 filled between the TFT substrate 200 and the color filter substrate 100. Here, each pixel of the TFT substrate 200 is provided with an indium tin oxide (ITO) 210 as an electrode.
The color filter 300 is provided in a flat matrix formed on the color filter substrate 100, including a red filter 330, a green filter 320 and a blue filter 310 with good light-transmissivity. Ways of arranging the color filter 300 are different according to the LCD assemblies, and includes a mosaic arrangement, a triangle arrangement, a straight line arrangement, etc. Here, the color filter 300 is required to have high chromatic density and high light-transmissivity, be not discolored by the backlight (not shown), be chemically stable, and do not interact with the liquid crystal 400.
Further, the color filter 300 is classified into a dying type and a pigment type according to materials of an organic filter, and is fabricated by a dying method, a dispersion method, an electrodepositing method, a printing method, etc. Currently, in the case of the LCD assembly using the TFT, the dispersion method is popular in making the color filter 300. Here, the color filter 300 fabricated by the dispersion method comprises photoresist elements for a photopolymerization such as a photopolymerization initiator, a monomer, a binder, etc., and organic pigments for the colors.
Here, to make a display unit get a larger size, be improved in property such as high fineness, etc., and maximize a color perception, a photolithography process is used when patterns of the red, green and blue color filters are formed. Particularly, the photolithography process is very important because the color filter 300 performs optical-filtering with a remaining color layer to maximize the chromatic cognition of the display unit.
As a process for forming the patterns, the photolithography process is divided into a photo process and an etching process. In fabricating the color filter 300, the photolithography process allows various materials coated on a wafer to form the color filter patterns. That is, a photoresist polymer is applied to a substrate and is then developed when exposed to light shining through a photomask, so that the photoresist polymer has a desired pattern. Thereafter, the substrate covered with the photoresist polymer having the desired pattern is etched, thereby forming the color filter pattern thereon.
Here, chromaticity property of the color filter 300 is realized by using a photopolymer and a color photoresist having dispersed pigments. In this case, high chromaticity and high brightness of the LCD assembly are realized by using a high transmissive pigment and increasing pigment-dispersed density.
However, as the pigment-dispersed density of the color photoresist is increased, the stability of the photoresist is decreased, the process of fabricating the color filter is complicated, and the film thickness of the color filter is increased. Therefore, a manufacturing process of the conventional LCD assembly is unstable and polarizability for light is lowered, thereby deteriorating the chromaticity property of the LCD assembly.
FIG. 2. illustrates a color reproduction of the conventional LCD assembly using the color photoresist and an American national television system committee (NTSC) standard in an international commission on illumination (CIE) system specified by CIE. Here, the CIE system shows a CIE chromaticity diagram based on three spectral stimulus values measured by a spectrophotometer, wherein three spectral stimulus values of stimulating the optic nerves with respect to red, green and blue colors are defined as X, Y and Z, respectively.
As shown in FIG. 2, the color reproduction of the conventional LCD assembly using the color photoresist meets the NTSC standard in red and blue regions of the CIE chromaticity diagram, but falls short of the NTSC standard in a green region because X and Y of the conventional LCD assembly are 0.25 and 0.60 and X and Y of the NTSC standard are 0.21 and 0.70.
To meet the NTSC standard in the green region, there is needed a color filter thicker than the conventional color filter by four times. However, as shown in FIG. 3, if the pigment-dispersed density for the green color is increased by four times, the light-transmissivity is lowered and the process stability is decreased because of a low containing ratio of the binder and the dispersing agent in the process of fabricating the color filter.